Signal receiving system



April 14, 1942. G. w. FYLER 2,279,819

SIGNAL RECEIVING SYSTEM 7 Filed June 15', 1936 .2 Sheets-Sheet 1 FAD/0 fe5auavcr Paer/a/mfaw/me T Inventor:

George W. Fyler,

b y Hi 7 Attow ney.

S IGNAL RECEIVING SYS TEM- Filed June 13,. 1956 2 Sheets-Sheet 2 Rho/0 Feeauavcy POE7/0/V 0F Pam/5e Inventor.

George W. Fyl r, by

H i s Attorney.-

Patented Agata 1942 SIGNAL RECEIVING SYSTEM v George W. Fyler, Stratford, Conn., assignor to General Electric Com New York pany, a corporation of Application June 13, 1936, Serial No. 85,077

26 Claims. (01. 250-20) My invention relates to signal receiving circuits and more particularly to means for use therein to reduce the reception of undesired noise currents, static, and the like. It has for one of its objects to provide improved means for reducing the reception of undesired noise currents.

In copending application Serial No. 85,083, filed June 13, 1936, by I. J. Kaar for Signal receiving system, now Patent 2,207,587, and which attenuated.

My inventin relates to devices of this character and it has for one of its objects to effect certain improvements therein whereby these devices are rendered more practical.

A further object of my invention is to provide means whereby the desired attenuation of noise currents dependently upon their relation to the intensity of the received carrier may be efiected without the use of a grid controlled discharge device.

A further object of my invention is to provide means whereby the desired attenuation may be effected with a minimum of equipment and cost.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which Figs. 1, 2, 3, and 6 represent different embodiments of my invention, and Fig. 4 represents in greater detail the applicais assigned to the same 'assignee as my present 10 of the carrier wave to be applied to the detector application is disclosed a device of the type re- I. If the receiver be one of the superheterodyne ferred to which operates to reduce reception of type this carrier wave may be the intermediate undesired currents only when said currents have frequency utilized in such a receiver. If desired, an intensity relative to the intensity of the reof course, the radio frequency received from the ceived carrier corresponding to more than a preantenna may be applied directly to the p ry 0f determined percentage of modulation of said carthe transformer, the transformer then, of course, rier, as for example 100% modulation. being tuned to the frequency of the receiver Since the device reduces only currents having carrier wave. Resistances 2 and 3, of course, intensity in excess of that value which modulates comprises the load resistance of the detector I the received carrier at any instant by more than and are shunted by a condenser 6 in the usual the predetermined percentage modulation, it is way whereby the voltage upon resistances 2 and inefiectiveto reducedesired signal currents even 3 varies in accordance with the envelope of the though they be of strong intensity, it being asreceived carrier wave. The audio frequency sigsumed, of course, that the received'carrier is nal currents are taken from load resistance 3 never modulated by desired current in excess of through conductors indicated at I and are supthe predetermined percentage of modulation. plied to any suitable load device such as an In this way during periods of reception of weak audio amplifier, headphones or loudspeaker. carrier even weak undesired currents are attenu- Diode 8 is similar to diode I and is provided ated whereas during periods of reception of a in accordance with my invention for the purstrong carrier only strong undesired currents are pose of reducing undesired noise currents. It

has its anode connected between the two resistors 2 and 3 and its cathode connected to a point between a resistor 9 and condenser Hi, the latter elements being connected in series across the diode load resistance 2, 3. The condenser III lated and thus the cathode of the diode is maintained at ground potential for these currents.

0 With respect to the average potential which appears upon the diode load resistance, however, the cathode of diode 8 is maintained at the same potential as the cathode of the diode I.

It will thus be seen that the cathode of the diode 8 is biased positive with respect to the anode with the result that the diode 8 is normally non-conducting. The anode potential of the diode varies with respect to ground in accordance with the instantaneous potential on the resistance 3 with the result that if the received carrier wave be modulated in excess of a predetermined percentage of modulation the potential of the anode becomespositive with respect to the cathode of the diode 8. In this event the diode becomes conducting and completes a Capacitor l0 should, of course, be of suificiently large capacitance that the voltage across it is not materially increased by the short static impulse.

After cessation of the static impulse, this condenser discharges through resistance 9;

For a specific example let us assume that during reception of a normal carrier 10 volts appears ,aavasio Y diode I is grounded. Its operation is similar to that explained in connection with Fig. 1. The average value of the electromotive force on resistance 2 is supplied through resistance 3 to the When this instantaneous voltage attains .a value across each of resistances 2 and 3. The cathode of diode 8 is then 10 volts positive with respect to the anode thereof with the result that this discharge device is normally non-conducting and ineffective to attenuate signal currents irrespective of their intensity, provided the carrier is not modulated by more than one hundred percent.

If, however, an impulse of static be received having such an intensity. that the instantaneous voltageon each of resistances 2 and 3 rises to 20 volts then the anode of the diode attains. a po-' tential equal to that of the cathode sincethe cathode potential cannot change at the instantaneous rate by reason of'condenser HL.

Thus for such static, or any stronger static, .or i

other undesired noise currents, the diode 8 is conductive and the undesired'current impulse is shunted about the resistance 3 through condenser It) to ground.

Letus assume now that the received carrier is of such intensity that fifteen volts appear across each of resistances 2 and 3.

stantaneous voltage on resistances 2 and 3 is that produced by rectification of the modulated carrier plus that produced by static, or other undesired noise currents. The component of this voltage produced by rectification of the carrier varies with the signal. age of modulation lessthan one hundred percent the instantaneous value of this component varies from a very small minimum value during negative peaks of modulation to large maximum values near but less than twice the carrier during positive peaks of modulation. Thus the intensity of static which is suflicient to cause the device 8 to become conductive is dependent upon the time when it arrives with respect to the signal modulation of the carrier but in the system described in which resistances 2 and 3 are mentioned as equal it must be such that the total instantaneous voltage on the diode load has a value corresponding to at least one hundred percent modulation of the carrier.

Of course, if the static, or undesired noisecurrents, ,which cause diode 8 to become conductive are sufliciently persistent, the charge oncon- If we assume a percent- The static impulse must now be of such intensityas to inresistance is applied thereto.

double the average value of the carrier, that is, exceeds a value corresponding'to 100% modulation of the carrieifiidevice 8 becomes of low impedance and produces an effective shunt across resistance 3. The signal may then be taken from resistance 3 as indicated by conductors I.

Fig. 3 represents a form of the invention in which the static eliminating elements 8, 3 and ill of both of Figs. 1 and 2 are applied to the single diode load resistance ll of Fig. 3. It so happens that if the static. eliminating arrangements of Figs. land 2 both 'be applied to the same diode load resistance and the two discharge devices be arranged to become conductive in response to the same currents, than equal and opposite currents flow to the intermediate .point on the diode load resistance with the result that this connection to the intermediate point may be eliminated. The two'diodes 8 are thus, in effect, connected in series between the two points on the two branches comprising elements 9 and III, the two diodes thus serving merely the function of a single diode, and: may be replaced by the single diode 8 of Fig. 3. Certain advantages, however,

result from such an arrangementin that the function of the two diodes of the circuits of Figs. 1 and 2 is accomplished by a single diode and in addition this single diode is biased by the entire voltage across the diode load resistance and the instantaneous-voltage of the entire diode load In addition the output signal may be taken from across the entire resistance .ll of the diode I whereas in Figs. land 2 it may be taken only from but a portion of this resistance, namely, resistance 3,

by reason of the fact that in those figures the I noise currents which flow through diode 8 also denser l0 may materially increase thus increasing the value of instantaneous voltage necessary to cause the diode 8 to become conductive.

Fig. 2 is similar to Fig.1 and differs therefrom in that the diode 8 is reversed with respect to Fig. 1 and the resistance 9 and condenser III are interchanged in position. Also the cathode of appear in resistance 2. Thus it will be observed that the arrangement of Fig. 3 possesses definite advantages over the arrangements of Figs. 1 and 2.

In this arrangement, however, the capacitors l0 and ID are in series across the diode load resistance and-hence must have correspondingly larger capacity to avoid an increase'in the rate at which they ,becornecharged during intervals of persistent static.

Fig. 4 represents the invention of Fig. 1 applied to a well known diode circuit of a super heterodyne receiver employing automatic volume control and automatic frequency control of the local oscillator. The portion of this receiver prior to the last intermediatefrequency transformeris represented by the rectangle l2. The

last intermediate frequency transformer comprises the primary winding l3 and secondary winding Ill, these windings of course being tuned by respective condensers l5 and [6 to the intermediate frequency. The primary winding-ls connected ina path between the midpoint of secondary winding I4 and ground through conand the righthand terminal is connected to ground through diode 20 and condenser 2|, the cathodes of these two diodes being connected together through resistances 22, 23, and

' is also connected to a point between resistances 23 and 24 for unidirectional current through a path including resistances 29, 3| and 9 for automatic volume control purposes. Discharge device 30 is of the variable mu type and employs a condenser 32 between its anode and control grid whereby the input'capacity varies with the unidirectional voltage on the control grid. This capacity may cooperate with resistance 29 to form a resistance capacity filter thereby variably to attenuate currents in the high frequency portion of the voice or music range' all as disclosed in my copending application Serial No. 68,181 which is assigned to the same assignee as my present application.

Since primary winding l3 and secondary winding M are both tuned to the intermediate frequency the voltage on the secondary winding is displaced in phase by 90 from that on theprimary winding. Thus the voltage on one half of this winding lags the primary voltage by 90 whereas that on the other half leads the primary voltage by 90. By the connection described the voltage on the primary plus that on half of the secondary is applied to the diode l9 for rectification thereby and the voltage on the primary plus that on the other half of the sec- -ondary I4 is applied to the diode 2| for rectie fication thereby. These phase relations, however, are present only when the intermediate frequency is exactly at the frequency to which the primary and secondary are tuned. .The secondary voltage shifts in one direction or the other dependently upon the direction in which the frequency shifts and accordingly if the frequency reduces, with the connection described, the voltage applied to one of the diodes l9 and 2| reduces while that applied to the other increases,

whereas if the frequency increases the reverse occurs.

Currents in diode |9 flow through resistances 22 and 23 in a direction opposite to the direction in which current in diode 2| flows through resistance 24. If these currents be equal no voltage appears between the cathodes of the two discharge devices I9 and 20. The left end of resistance 22 is connected to ground with the result that the right end of resistance 24 becomes either positive or negative with respect to ground in accordance with the variations in the intermediate frequency. Accordingly the voltage at the right end of resistance 24 may be supplied through a conductor 33 to any suitable instrumentalities not shown, such as a properly connected discharge device for automatically controlling the frequency of the local oscillator to maintain the intermediate frequency constant. One means whereby this control may be effected is described in application Serial No. 76,789 of R. B. Dome which application is assigned to the same assignee as my present application.

The voltage at the point between resistances 23 and 24 is negative with respect to ground during the. reception of a received carrier wave by an amount dependent upon the intensity of the received carrier and hence may be applied through a resistance capacity filter 34, to the grids of amplifiers employed in the receiver l2 for automatic volume control purposes.

Resistance 9 corresponds to the resistance9 of Fig. 2 and similarly condenser I9 corresponds to condenser of Fig. 2. The diode 3, resistance 9, and acondenser ID are connected to the load resistance 22, 23 of diode I9 in the same way as is done in connection with Fig. 2 and the operation is exactly as described in connection with Fig. 2.

In the forms of the invention shown in Figs. 1 to 3 the static reducing arrangement operates to shunt the undesired currents about the portion of the load-resistance across which the signal load is connected. I shall now describe in connection with Fig.5 a form of my invention in which the signal load is effectively opened during the presence of undesired currents having intensity corresponding to a value in excess of a predetermined percentage of modulation of the carrier.

In the form of the invention shown in Fig. 5 the portion 2 of the diode load resistance 2, 3 is shunted for direct currents by a path comprising resistances 31 and 38 and diode 39, the point 42 between resistances 3 1 and 33 being connected to ground throughcondenser which has low reactance to currents of'the signal frequency. As thus described it will be observed that during reception of a carrier wave the anode of the diode 39 is connected through resistances 38 and 31 to a point on resistance 2 which is positive with respect to the cathode of diode 39 with the result that current flows through diode of resistances 38 as indicated by conductors H and hence in series with diode 39.

Let us assume now that an impulse of static be received which has an intensity corresponding to a precentage of modulation in excess of a predetermined amount.. The cathode of the diode is driven positive by the impulse of static, to a value, let us say, at least twice as great as the average voltage on resistance 3. The lower terminal of resistance 31, however, cannot vary at the static rate by reason of the time constant of resistance 31 and condenser 40 with the result that the potential of the cathode of diode 39 attains the potential of point 42 and the voltage across resistance 30disappears. comprisingthe arms 2, 3, 31 and 40 is then/balanced and no current flows in its diagonal 39, 39. Thecdiode 39 is therefore no longer conducting. Thus during such times no currents. appear in resistance 38 and the impulse of static is thus prevented from reaching the load circuit.

For a particular example let us assume that resistance 2 is 500,000 ohms, resistance 3 is 250,- 000 ohms, and resistances 31 and 38 are each 2 megohms, and let us assume that a normal car- The bridge rier. produces 10 volts on resistance 3 and 20 on resistance 2. This means that during such reception the point 42 is 10 volts positive with respect to the cathode of diode 39 and condenser 40 is charged to 20 volts.

Now let us assume that an impulse of-static is received causing the voltages on resistances 2 and 3 to at least double. Then the cathode po-' tential of diode 39 attains or exceeds the potential of point 42 with the result that the cathode of diode 39 is no longer negative with respect to point 42 and thus diode 39 becomes non-conducting and the static impulse-is prevented from reaching the circuit 4I.

It will of course be seen with the arrangement shown in Fig. 5 that during the intervals when static impulses are received and discharge device 39 is non-conductive that condenser 40 tends to charge through resistance 31 to the full voltage of the diode load resistance 2, 3 with the result that if the static charges are sufficiently persistent the condenser 40 becomes so charged that the reduction of static or noise currents produced by the arrangement is greatly reduced. It is necessary, however, to proper operation of the diode I that resistances 31 and 38 be high as for example of the value of 2 megohms mentioned although I have employed at 31, for example, a resistance of 1.2 megohms and at 38 a resistance of .33 megohm, the capacitance of condenser 40 being so chosen with respect to resistance 3'! that the time required for charging the condenser 40 extends over a considerable period. Thus the device is very eifective in reducing static, particularly static clicks, or impulses of shozt duration.

In this respect the arrangement of Fig. 5 possesses advantages over those of Figs. 1 and 2. For example in Fig. 1 when diode 8 becomes conducting condenser IO starts to charge through resistance 2, which may be 250,000 ohms, and the low resistance of the diode. The more it charges the less effective the devicebecomes in eliminating static. When the static pulse ceases it is desirable that the condenser discharge as rapidly as possible through resistance 9. Therefore this resistance must be chosen as low as possible consistent with proper operation of diode I during reception of strongly modulated signals, but should be four or five times the sum of the resistances of resistors 2 and 3. This is necessary in order that a high ratio exist between the alternating and-direct current load impedance of diode I thereby to avoid distortion which occurs during reception of carriers having a high percentage of modulation if such a high ratio between these impedances does not exist.

' my invention it will of course be understood that In the system of Fig. 5, on the other hand,

during a static impulse condenser 40 tends to charge through resistance 3'! which may be 2 megohms. After the static pulse ceases the condenser discharges through resistance 38 which may be two megohms. Thus the time constant of the discharge path is less than that of the charge path with the arrangement of Fig. 5 rather than much greater with-that of Fig. 1. Fig. 5 has been found to be the more effective arrangement in reducing static.

Fig. 6 is similar to Fig. 5 but differs therefrom only in that the cathode of diode I is grounded directly, the anode in this figure being connected to ground through resistances 2 and 3. The diode 39 is so polarized by the potential on resistance 2 that it is conducting normally but becomes non-conducting when the potential on instantaneous resistance 3 attains aninstantaneous value in excess of the average value oi the potential of the cathode oi- ..resistance 33 with respect to ground. The'load device such as the high impedance grid circuit, of an electron discharge audio amplifier may be connected to the resist.- ance 33 as indicated by conductors 4|.

If the diode 39 of Fig. 6 be of the so-called metal type, that is, one in which the electrodes are housed within a metallic shell, it is preferable that the metallic shell be connected to the negative end of resistance 38 whereby when the tube is conducting the shell is always negative with respect to the cathode and hence no electrons flow to the she l.

While I have shown particular embodiments of I do not wish to be limited thereto since many modifications both in the circuit arrangement and in the instrumentalities employed may be made and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The combination, in a receiver for modulated carrier waves, of a detector for said carrier wave having a load impedance, a signal load connected across at least a portion of said impedance, and means for supplying current from said loadimpedance to said load only when said currents have intensity corresponding to less than a predetermined percentage of modulation of the received carrier wave, said means including a diode, means to supply bias voltage to said diode varying in response to the average value of the received carrier wave, and means to supply signal and noise voltage from the output of said detector to overcome said bias voltage, said bias voltage being overcome when the noise or signal voltage is of a value relative to the average value of the received carrier corresponding to more than a predetermined percentage 01' modulation of the carrier, the variations of said bias voltage maintaining said predetermined percentage of modulation fixed over a wide range of average intensities of the received carrier wave.

2. The combination, in a receiver for modulated carrier waves, of a detector for said carrier wave having a load impedance, a signal load connected across at least a portion of said impedance, a diode connected to said signal load and load impedance, means utilizing said diode to reduce the transmission of current to said signal load from said load impedance in response to intensities of current on said load impedance in excess of a value corresponding to a predetermined percentage of modulation of the received carrier wave, and means to maintain said predetermined percentage of modulation fixed in response to'variations of the average value of the carrier over a wide range of variation thereof.

3. The combination, in a receiver for modulated carrier waves,of a detector for said carrier wave having an output circuit for demodulation products, .a diode connected to said circuit in such a way as to control the flow of current to said circuit in accordance with the condition of conductivity of said diode, and means responsive to the relation between the average intensity of the carrier wave pplied to said detector and the intensity of currents applied thereto to control the conductivity of said diode. 4. The combination, with a detector having a. load impedance, of a shunt path across a portion of said impedance including a resistance and a condensenin series, and a diode connected between an intei'mediate point on said portion or said impedance and a point between said condenser and resistance, said condenser having low impedance to currents of the frequency detected by said diode, whereby voltage. from one portion oi said impedance is applied to said diode as a bias and the instantaneous voltage of the other section of said impedance is applied to said diode as a control voltage, said diode being so poled that its conductivity changes when said instantaneous voltage overcomes said bias, and means to receive signals from the portion of said impedance nearest said condenser dependently upon the conductivity of said diode.

5. The combination, with a detector having a load impedance, of a shunt path across a-por- 'tion of said impedance including a resistance and a condenser in series, and a diode connected between an intermediate point on said portion of said impedance and a point between said condenser and resistance, said condenser having low impedance to currents of the equency detected by said diode, whereby voltage from I one portion of said impedance" is applied to said diode as a bias and the-instantaneous voltage of the other section of saidimpedance-is applied to said diode as a control voltage, said diode being so poled that it is normally noneconductive tion of said impedance including a resistance and a condenser in series, and-a diode connected between an intermediate point on said portion of said impedance and a point between said condenser and resistance, said condenser having low impedance to currents of the frequency detected by said diode, whereby the voltage of one portionof said impedance is applied to said diode as a bias and the instantaneous voltage of the other section of said impedance is applied to said diode as a control voltage, said diode being so poled that it is normally conductive and becomes non-conductive when said instantaneous voltage overcomes said bias voltage, and a signaldevice connected in series with said diode.

'7. The combination, in a'carrier wave receiver the incomingpulsating voltage, andmeans for impressing upon said device a differe'iitproportion or said incoming pulsating voltage in opposition to said first mentioned proportion of said carrying pulsating direct signal current, the'combination of a by-pass ground circuit comprising a take-oft connection with said circuit means, a

bias controlled rectifierhaving its cathode. fed by said connection'and its anode connected through anode for an interval exceeding the normal duration of peak-type'electrical interferences.

10. The combination, in a radio receiver ha v ing an electron discharge device having an anode:

and a cathode, and a load resistance, means-to apply signal and noise electromotive force to said discharge device to produce current'variations in i said resistance in accordance with desiredsig nals and noise, the current in said resistance increasing in accordance with noise, pulses of one polarity, and decreasingto zerofi'n accordance with noise pulses of an .oppositefpolarity, means to supply electromotive force from; s'aidresistof a resistance having desired unidirectional curependent upon the intensity ofthe reance to a subsequent signal circuit jlin said receiver, and a unilateral conductingdeviceinsaid :circuit biased normally to passsignal current of normal intensities and polarized to become nonconductive inresponse to noise pulses of said one polarity, whereby noise pulses of said one polarity are limited by said unilateral conducting device and noise, pulses of the opposite polarity are lime ited by said first discharge device.

11. In combination, a resistance upon which signal and noise pulses of one polarity appear,

an audio load circuit including a diode having its cathode connected to a point on said load re sistance and its anode connected through a sec- OildflGSiSfifiljlCQ toanother point on said resistance whereby sig'nalelectromotlve force on said load resistance is transmitted through said diode to said second resistance, means to bias the electrode of saidfidiode remote from said first res sistance to'rendersaid diode conductive during presence of signal electromotive force of normal depending upon the desired modulations of said carrier, a diode having'an anode and cathode, means to bias said anode negatively with respect to said cathode from at least a portion of said resistance, means to apply voltage varying with intensityfand saiddiode being so poled that in the presence of noise pulses on said first resistance exceeding. said signaljsaid bias is overcome v the voltage on said condenser, and a second elec-' trode, means to supply voltage between said second electrode and said one sideof said circuit 8. Iiieonibination with a circuit carrying pulsating trol de ice operable to control the effective imect current, a non-linear electrical con'- pedance of said circuit, and means for estab-f lishing a threshold voltage for said device comprising means for impressing upon said device and said diode becomes non-conducting Y 12. The combination, in .a noise reduder, ,:of a circuit acrcss wliich unidirectional signal and noise electromotive force of varying amplitude appears, a resistance and a condenser connected across said circuit in series, a diode having one electrode oonnected'between said resistance and condenser whereby the voltage thereon with re,- spect to one side of said oirouitis determined by varyingin accordance with instantaneous signal portioned relative to each other that the voltage on said condenser remains substantially constant during short noise impulses between said one side of said circuit and said second electrode whereby the conductivity of said diode is dependent upon the relation between the voltage on said condenser and the instantaneous signal electromotive force in said circuit, and a conducting path for noise ,pulses through'said condenser and diode across said circuit when said diode is conducting.

13. Thecombination, in a noise reducer, of a circuit across whichtunidirectional signal and fznoise electromotive forces exist, a condenser and a resistance in series across said circuit, a diode having one electrode connected between said con,-

denserand resistance, and ascond electrode, means to supply signal and noise impulses between said -second electrode and one side of said circuit, said aresistarice and condenser maintaining a bias onsaid condenser sufficiently great and of such polarity as to. maintain said diode nonconducting-in the absence of noise pulses exceeding the signal in intensity, and a conducting path noise and signal rate, and means to store said unidirectional signal and noise electromotive force to produce a bias voltage, means to supply said bias voltage between the other electrode of said diode and said one side of said circuit with such polarity that said diode is non-conducting in the absenceof noise currents, the value of said bias being suchthat it is overcome by noise pulses in excess oi'the signal, wherebyisaid diode becomes conducting.

15. In combination, a circuit carrying unidirectional signal and noise pulses, aconnection across said output circuit, and means for changing the wave form of oscillations supplied from said first named means through said first and said second unidirectional current conducting paths to said output circuit, said last named means including means for producing a unidirectional potential drop across said resistor.

18. In combination, an electron discharge device having an anode, a cathode, and a load resistance, means to apply electromotive force of varying intensity to said discharge device to produce current variations in said resistance in accordance therewith, the current in said resistance increasing in accordance with electromotive force of one polarity, and decreasing to zero in accordance with electromotive force of the opposite polarity of greater than a'predetermined intensity, means to supply electromotive force from said resistance to a load circuit, and a unilateral conducting device in said circuit biased to pass current of normal intensity and polarized to become non-conductive in response to electromotive force of said one polarity greater than a second predetermined intensity, whereby electromotive force of said qne polarity and greater than said second predeterminedintensity is limited by said unilateral conducting device and electromotive force of the opposite polarity and greater than said first predetermined intensity is limited by said discharge device.

19. In combination, a resistance upon which electromotive force of one polarity and of varying intensity appears, a load circuit lncludinga diode having one electrode maintainedat a fixed potential with respect to a point on said resistance and its other electrode connected through a load r impedance to another point on said resistance, whereby electromotive force on said resistance is transmitted through said diode to said load imsaid circuit including a diode, means to vary the potential between -one.electrode ofsaid diode andone side of said circuit at the noise-and signal rate, a c'ondenserbetweehsaid other electrode of saiddiode and said oneside of said circuit, and means to maintain a charge in said condenser derived from said unidirectional signal. and noise pedance, means to 'bias said diode to render it conductive during presence of electromotive force on said reslstanceof les than a predetermined intensity, and said diode being so poled that in pulses to bias said electrodes from each other by i an amount such that said diode is non-conducting during the presence of signals but becomes 4 ezrcess of the signal.

the presence or electromotive force or greater than said predetermined intensity. on said received radio frequency currents into audible sig- 16. In combination. a circuit carrying unidirectional signal and noise pulses, a diode, means to supply unidirectional potential from said circuit to one electrode of. said diode with a storing action, means to vary the potential of the other electrode of the diode at the signal and noise rate-the relative values of said potentialsand the polarity of said diode being such that the condition of said diode with respect to conductivity and non-conductivity is unchanged during the presence of normal signals and is changed in response to noise pulses in excess of normal signals, .a load, and means to supply signal current from said circuit to said load dependent-upon the conductivity of said diode.

17. In combination, a first unidirectional current conducting path,-means for producing alternating current oscillations in said first unidirectional current conducting path, a second uni-q directional current conducting path, a resistor second unidirectional current conducting path to the bridge c .nals substantially free from noise impulses that may be impressed simultaneously with the signals upon the radio receiving system, comprising a first rectifier for rectifying the received currents, a bridge circuit, said first rectifier being connected as a diagonal of said bridge circuit, a second rectifier connected to the other diagonal of the bridge circuit, said second rectifier being biased so asto block the passage of all currents therethrough when noise impulses are impressed upon uit, and means for translating the signals traversing said second rectifier when substantially no noise impulses are impressed upon the system.

21; In a radio receivingsystem for discriminating against noise impulses or large amplitude. means for rectifying all of the currents impressed upon the system, a bridge circuit one or the diagonals of which is supplied with the rectified I current, adetector, a resistor connected in series with said detector across the opposite diagonal of tected'by said detector will traverse said resistor. and an amplifying device connected across 'said resistor for amplifying only those voltages appearing across said resistor.

22. The combination or means for receiving signal currents as well as noise impulses, a Wheatstone bridge circuit to which said receiving means is connected as one diagonal thereof, detecting means connected as the other diagonal of said bridge circuit, means responsive to said signal currents for applying through said bridge circuit voltages of one polarity for detection by said detecting means, and means responsive to said noise impulses for applying voltages of the opposite polarity through said bridge" circuit to said detecting means to render said detecting means inoperative.

23. In combination, a source of unidirectional electromotive force modulated in accordance with signals and noise, a noise limiter comprising a resistance and a condenser connected in series across said source and a, unilateral conducting device connected between a point on said source and a point between said resistance and con- 7 denser, whereby the charge on said condenser increases during a noise pulse and decreases after termination of said noise pulse, and means to render the time constant of the path through which said condenser is charged during a noise pulse, at least as long as the time constant of the path through which it discharges.

24. Apparatus for eliminating undesired peaks from signal voltages having, in combination, a rectifier, means whereby the rectifier rectifies the signal voltages to obtain a rectified signal voltage of predetermined polarity and suppresses the signal voltages of the opposite polarity, a second rectifier, means for establishing a current in one direction through the second rectifier to render the second rectifier conducting in the opposite direction, means for transmitting the signal currents through the second rectifier in the said opposite direction, and means for stopping the current to render the second rectifier non-conducting in the said opposite direction when the voltages of the currents to be transmitted through the second rectifier attain values corresponding to the peaks to be eliminated from the signals.

25. Apparatus for transmitting along a. path signal voltages not greater than a desired magnitude and suppressing signal voltages greater than the said magnitude, the said apparatus having, in combination, means for rectifying the signal voltages to obtain a rectified signal voltage of predetermined polarity, means for impressing upon the path a unidirectional voltage of substantially the said magnitude to establish in the path a unidirectional current for rendering the path conducting in one direction to the rectified voltages not greater than the said magnitude and non-conducting in the said direction to the rectified voltages greater than the said magnitude, and means for transmitting the rectified voltages along the path in the said direction. a

26. In a noise eliminating system for high frequency' receivers, the combination of means to rectify the received high frequency oscillations and to produce a unidirectional signal voltage varying with variations in intensity of the received oscillations, a unilateral conducting device,

means to supply a bias voltage to said device.

poled to render it conductive, means to supply said unidirectional signal voltage to said device poled to render it non-conductive, and a signal load device in series with said unilateral conducting device, whereby current in said signal load device varies in accordance with said signal voltage and is zero in value when said signal voltage exceeds said bias voltage.

GEORGE W. FYLER. 

